It is known to modulate an optical carrier with a signal, using amplitude modulation, frequency modulation, or polarization modulation. U.S. Pat. No. 3,571,597 illustrates a system in which a signal is transmitted via an optical carrier and simultaneously an RF reference signal is also transmitted for the purpose of maintaining phase stabilization between the originating location and the remote location, so that the system is not completely optical. Many systems are known in the prior art that combine a signal with a reference signal, for the purpose of providing a more stable and effective method of transmission. These prior art systems have a common feature in that the signal transmitted has a frequency sufficiently low that it does not cause difficulty in modulating the optical carrier.